Recovery of nickel and molybdate from ammoniacal leach liquors of spent HDS catalysts using chelating ion exchange resin

Abstract

Spent hydrodesulphurization (HDS) catalysts containing valuable Mo and Ni ions are potential source for the recovery of Mo and Ni from the point of commercial, environmental and conservation of natural mineral resources. In the present study, oxidative roasting of spent HDS catalyst followed by ammonia leaching results in the leach liquor with about 15.3 g/L Mo (~85% recovery), ~125 g/L (NH4)2SO4 and ~0.9 g/L Ni as impurity. Therefore Ni separation from this ammoniacal molybdate leach liquor is essentially the first step to obtain high pure molybdate and ammonium sulfate solution. In this study, separation of nickel from ammoniacal molybdate leach liquor was reported using commercial chelating iminodiacetate resin, Lewatit TP207 by batch and column methods. Optimization of process parameters include equilibration time, acidity of leach liquor, aqueous flow rate, metal concentration, loading capacity of resin for Ni during sorption of Ni, desorption of nickel from loaded resin and stability and reuse of resin in continuous column experiments. Feed leach liquor of pH >8.0 is important to achieve clear separation of Ni from Mo. Loading capacity of resin and break through curves are optimized to achieve <10 mg/L Ni in purified Mo leach liquor and further processing results in high grade ammonium octamolybdate (AOM) and ammonium sulfate crystals. Finally, a process flow sheet for the complete separation and recovery of Ni, Mo and ammonium sulphate with material balance from ammoniacal molybdate leach liquor of spent HDS catalyst was demonstrated for possible industrial application.